The present invention relates to a high-sensitivity flexible ceramic sensor having usefulness as an acceleration sensor for the air bag systems of automobiles and as a vibration sensor used for the measurement of high vibrational frequencies.
As is known, ceramic sensors are widely employed as an acceleration sensor for detecting the acceleration of an automobile caused by an accidental collision in order to bring the air bag system into operation or a vibration sensor for detecting abnormal vibrations of gas turbine blades and vibrations of high-speed vehicles due to troubles in the wheels and engines.
These ceramic sensors of which the sensing element is made from a ceramic material have a serious disadvantage in respect of mechanical strengths and heat shock resistance and are under a risk of destruction during use. As a means to alleviate this disadvantage, proposals are made to employ a sensing element made of a composite material consisting of a ceramic material and a plastic resin as a reinforcement of the ceramic material. This means, however, is necessarily accompanied by another problem due to a decrease in the sensitivity as a sensor.
The present invention has an object, in view of the above described problems in the prior art ceramic sensors, to provide a novel high-sensitivity ceramic sensor having high resistance against mechanical and thermal shocks to exhibit a high sensitivity with stability.
Thus, the high-sensitivity flexible ceramic sensor provided by the invention is an integral device which comprises:
a metal foil having flexibility;
a single-crystalline thin film of a piezoelectric ceramic material formed on one surface of the metal foil;
an electrode formed on the surface of the thin film of the piezoelectric ceramic material; and
an external electric circuit connecting the metal foil and the electrode.
In particular, the metal foil and the thin film of the piezoelectric ceramic material each have a thickness in the range from 5 to 1000 xcexcm and in the range from 0.2 to 10 xcexcm, respectively, and the piezoelectric ceramic material is selected from the group consisting of aluminum nitride, zinc oxide and lithium niobate.